KSZ9563RNXI-TR datasheet(33/226 Pages) MICROCHIP

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DS00002419D-page 33

KSZ9563R

4.4.3.2.1

Tag Insertion and Removal

Tag insertion is enabled on all ports when the VLAN feature is enabled. At the ingress port, untagged packets are tagged

with the ingress port's default tag. The default tag is separately programmable for each port. The switch does not add

tags to already tagged packets unless double tagging is enabled.

At the egress port, tagged packets will have their 802.1Q VLAN tags removed if un-tagging is enabled in the VLAN table

entry. Untagged packets will not be modified if 802.1Q is enabled.

4.4.3.2.2

Double Tagging

The switch supports double tagging, also known as Q-in-Q or VLAN stacking. This feature can be used for service pro-

viders to append a second VLAN tag in addition to a first VLAN tag applied by the customer. VLAN support can be

enabled either with or without double tagging. When double tagging is enabled, the outer tag is recognized and is used

for VLAN and address lookup instead of the inner tag. The outer tag precedes the inner tag in the frame header: the

outer tag is located immediately after the source address, and contains a different Tag Protocol Identifier (TPID) value

than the inner tag.

Additional controls are available for full control of the VLAN function. Some of these features can be enabled on a per-

port basis, while others are global:

• Ingress VLAN Filtering: Discard packet if VID port membership in VLAN table does not include the ingress port.

• Discard non PVID Packet: Discard packet if VID does not match the ingress port default VID.

• Discard un-tagged Packet: Discard any received packet without a tag.

• Drop tag: Drops the packet if it is VLAN tagged.

• Unknown VID Forward: Forward to a fixed set of ports if VLAN lookup fails.

• Drop unknown VID: Additional options for unknown VID packets: discard or forward to the host port.

• Null VID Replacement: Replace a null VID with the ingress port default VID.

• PVID Replacement: Replace a non-null VID with the ingress port default VID.

• Double Tag Mcast Trap: In double tag mode, trap all reserved multicast packets and forward to the host port.

4.4.3.3

VLAN Registers

Table 4-11 provides a list of VLAN related registers.

TABLE 4-11:

VLAN REGISTERS

Registers

Description

Switch Operation Register

Double tag enable

Switch Lookup Engine Control 0 Register

VLAN enable; Drop invalid VID frames

Switch Lookup Engine Control 2 Register

Trap double tagged MC frames;

Dynamic & status egress VLAN filtering

Unknown VLAN ID Control Register

Forward unknown VID

Switch MAC Control 2 Register

Null VID replacement with PVID at egress

VLAN Table Entry 0 Register,

VLAN Table Entry 1 Register,

VLAN Table Entry 2 Register,

VLAN Table Index Register,

VLAN Table Access Control Register

Read/write access to the VLAN table

Port Default Tag 0 Register,

Port Default Tag 1 Register

Port default tag

Port Ingress MAC Control Register

Drop non-VLAN frames; Tag drop

Port Transmit Queue PVID Register

PVID replacement at egress

Port Control 2 Register

VLAN table lookup for VID=0;

Ingress VLAN filtering; PVID mismatch discard

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